Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. A common technique for forming the circuitry on a semiconductor wafer is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by inconsistencies or unevenness in the wafer surface. This sensitivity is accentuated with the current drive for smaller, more highly integrated circuit designs which cannot tolerate certain nonuniformities within a particular die or between a plurality of dies on a wafer. Because semiconductor circuits on wafers are commonly constructed in layers, where a portion of a circuit is created on a first layer and conductive vias connect it to a portion of the circuit on the next layer, each layer can add or create nonuniformity on the wafer that must be smoothed out before generating the next layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a polishing pad moving in the plane of the wafer surface to be planarized. The polishing pad used in the CMP process is typically a disk or a belt. In some systems, a polishing fluid, such as a chemical polishing agent or a slurry containing microabrasives, hereinafter referred to as a slurry for simplicity, is applied to the polishing pad to polish the wafer. The wafer holder then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer in order to create a smooth surface and remove any nonuniformities. The surface of the wafer is often completely covered by, and in contact with, the polishing pad to simultaneously polish the entire wafer surface.
Typical slurry dispensing systems include an elongated member, or manifold, located above the polishing surface of the polishing pad. The manifold has a plurality of nozzles formed thereon, or attached thereto, from which slurry is applied to the polishing pad by using a dripping method where the slurry is dripped onto the polishing pad from the nozzles, as shown in FIGS. 9 and 10B. As the slurry is dripped onto the polishing pad, trails of slurry are formed on the polishing pad. These trails of slurry are not distributed over the surface of the polishing pad until the trail comes into contact with the rotating wafer during the CMP process. One drawback to this method of slurry distribution is that these trails tend to cause an uneven wear rate across the surface of the wafer due to the fact that a large portion of slurry is concentrated at particular points along the polishing pad, and each of these trails is only dispersed over the surface of the polishing pad by the rotation of the wafer. This can cause rings of greater wear to form on the surface of the wafer as the wafer is rotated, which results in an uneven wear profile of the wafer surface. An uneven wear profile can cause problems for subsequent steps of semiconductor wafer production because the surface of the wafer is not smooth. Additionally, because the trails that are formed on the polishing pad have increased amounts of slurry, the life of the polishing pad is decreased due to the added wear that occurs as a result of the frictional contact between the rotating wafer and the moving polishing pad having localized areas of increased amounts of slurry. Accordingly, there is a need for a method and system to provide an even distribution of slurry onto the polishing surface of the polishing pad.